1. Field of the Invention
The present invention relates generally to a fluorescent lamp, and more particularly to a low wattage fluorescent lamp adapted to function with high frequency electronic ballasts already present in the marketplace.
2. Description of Related Art
T8 fluorescent lamps have become quite popular, and have largely supplanted the previous generation T12 fluorescent lamps due to their inherent higher efficiency. A typical 4-foot T8 fluorescent lamp using the known three component rare earth phosphor blends operates on the IES reference circuit at 32.5 watts (W) and All produces 2850 lumens or about 88 lumens/watt. On high frequency commercial electric ballasts, efficiencies are significantly higher.
It is desirable to improve the energy efficiency of T8 fluorescent lamps to consume less energy. Because lighting applications employing T8 lamps account for a significant portion of total energy consumption, an improved energy efficient T8 lamp will significantly reduce total energy consumption. Reduced energy consumption translates into cost savings to the consumer as well as reduced environmental impact associated with excess energy production necessary to meet current needs.
Consequently, there is a need for a low-wattage T8 fluorescent lamp having equivalent lumen output compared with standard T8 fluorescent lamps. One method of improving lumen efficiency is to add krypton to the fill gas of a fluorescent lamp. Unfortunately, the addition of krypton (especially beyond 40 vol. %) typically creates other problems, namely difficulty in lamp starting and lamp striations.
It is desirable to provide a fluorescent lamp that has a high proportion of krypton in the fill gas (i.e. greater than 40 vol. %) to achieve high lumen efficiency, wherein difficulty in lamp starting and striations are totally or substantially eliminated.
A low pressure mercury vapor discharge lamp is provided having a light-transmissive glass envelope having an inner surface, a pair of spaced electrodes, a phosphor layer coated adjacent the inner surface of the glass envelope, and a discharge-sustaining fill gas of mercury vapor and inert gas sealed inside the envelope. The inert gas has 40-100 vol. % krypton with the balance argon, and the total pressure of the fill gas inside the glass envelope is 0.5-3 torr at 25xc2x0 C. The lamp has a lumen efficiency of at least 80 lumens/watt.
A low-wattage lighting system is also provided having a mercury vapor discharge fluorescent lamp and a ballast. The ballast is adapted to electrically couple to the lamp, and the ballast has a striation killing electronic circuit. The ballast has a starting voltage of at least 500 volts. The lamp has a light-transmissive glass envelope having an inner surface, a pair of spaced electrodes, a phosphor layer coated adjacent the inner surface of the glass envelope, and a discharge-sustaining fill gas of mercury vapor and inert gas sealed inside the envelope. The inert gas has 40-100 vol. % krypton with the balance argon, and the total pressure of the fill gas inside the glass envelope is 0.5-3 torr at 25xc2x0 C. The lamp has a lumen efficiency of at least 80 lumens/watt.